1. Field of the Invention
This invention relates to fuser and pressure roller-type fusing stations for fusing toner images in an electrostatographic apparatus such as copiers and printers. More particularly, this invention relates to such a fusing station that includes a release-oil level detector.
2. Description Relative to the Prior Art
In electrostatographic apparatus such as copiers and printers, fuser and pressure roller-type fusing stations as disclosed for example in U.S. Pat. Nos. 4,870,445 and 4,870,446 issued Sep. 26, 1989 in the names of Collier et al. and Bickerstaff et al., respectively, are well known for fusing toner images on suitable receivers. Usually, the fuser roller of such a station is heated, and rotatably forms a fusing nip with an unheated pressure roller. A suitable receiver sheet with an unfused toner image thereon is fed through the fusing nip such that the heated fuser roller directly contacts and heats the toner image on the receiver sheet.
A common problem associated with such fusing stations is that the toner particles which form the toner image, partially offset undesirably from the receiver sheet onto the surface of the fuser roller. As disclosed, for example, in the patents cited above, and in commonly assigned U.S. Pat. No. 4,994,862, issued Feb. 19, 1991 in the name of the present inventor Linn C. Hoover, such an offsetting problem can be prevented by the application of release oil to the surface of the fuser roller.
Typically, a system for supplying and applying such release oil is mounted in a remote and blind location within a copier or printer, and includes a reservoir that can hold a substantial quantity of such oil. The oil is withdrawn from the reservoir by suitable means, and is used up by being applied to, and released from, the surface of the fuser roller. Eventually, however, the quantity of oil in the reservoir can all run out or be all used up, and if not replenished, can undesirably result in reoccurrence of the toner offsetting problem, and hence in poorly fused images from the fusing station. There is, therefore, a need for a simple and reliable release oil level detector for use in association with such a reservoir in order to prevent such a run out and reoccurrence of the toner offsetting problem.